Evaluation of vertical structure of cloud fraction simulated by IPCC AR4 models over TWP

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Description

Cloud Fraction (CF) is a critical variable in determining the radiation flux through the atmosphere and at the surface in the climate models. Previous studies in evaluating Global Climate Model (GCM) performance revealed that the model biases for both atmosphere and surface shortwave absorption are largest at lower latitude areas, suggesting a poor performance of GCMs in simulating CF over tropical regions. Combined CF data sets that represent both the vertical and horizontal CF are generally not available for evaluating the CF in large-scale models. Current techniques generally use either satellite or ground-based hemispheric measurements to estimate horizontal CF. Alternatively, vertical cloud occurrence is determined using time series of narrow-beam active remote sensors. In this study, we first inter-compare four CF-related data sets over TWP, i.e., the total sky cover based on Total Sky Imager, the Active Remote Sensing of Clouds Layers (ARSCL), the total sky cover derived from surface shortwave radiometers, and effective sky cover derived from longwave radiometers. We integrate these data sets and generate a new composite CF data set that includes vertical structure. We use the integrated CF data set to evaluate the CF, including its vertical structure, predicted by IPCC AR4 GCMs.